With the rapid growth of mobile communication and the great progress in technology, the world is becoming a completely inter-connected network society where anyone may obtain information and share data anytime and anywhere. It is estimated that by 2020, the number of inter-connected devices will reach 50 billion, of which only about 10 billion may be mobile phones and Tablet PCs and the rest are machines communicating with one another, rather with human beings. Therefore, how to design a system to support a large number of machine communication equipment is a subject in need of an in-depth study.
In the standard of Long Term Evolution (LTE) work item of the Third Generation Partnership Project (3GPP), machine-to-machine communication is called Machine Type Communication (MTC). MTC is a data communication service that does not require human participation. The large-scale deployment of MTC user equipment can be used in the fields, such as security, tracking, payment, measurement, and consumer electronics. Applications that are related to the deployment of MTC user equipment include video surveillance, supply chain tracking, smart electric meters, remote monitoring, etc. MTC requires lower power consumption and supports lower data rate and lower mobility. At present, the LTE system is mainly for human-to-human (H2H) communication services; yet, a key to achieve the large scale competitive advantage and application prospect of MTC service is that LTE networks support low-cost MTC equipment.
In addition, some MTC equipment needs to be installed in the basement of a residential building or at locations protected with an insulating foil, a metal window, or a thick wall of an existing building; as compared with conventional equipment terminals (such as mobile phones, tablet computers, etc.) in LTE networks, the air interfaces of such equipment will obviously suffer from serious penetration losses to a greater extent. The 3GPP has decided to study the solution design and performance evaluation of MTC equipment with additional 20 dB coverage enhancement. Note that MTC equipment located in poor network coverage areas has the following features: a very low data rate, a much more relaxed latency requirement, and limited mobility. The LTE network can further optimize some signaling and/or channels to better support MTC services regarding the features mentioned above.
In this respect, at the 3GPP RAN#64 convention held in June 2014, a new work item oriented on Rel-13 with even lower complexity and enhanced coverage MTC was proposed (see NPL: RP-140990 New Work Item on Even Lower Complexity and Enhanced Coverage LTE UE for MTC, Ericsson, NSN). In the description of this work item, the LTE Rel-13 system needs to support an MTC user equipment having 1.4 MHz RF bandwidth for uplink and downlink (hereinafter referred to as a narrowband MTC UE) to operate at any system bandwidth (e.g., 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, etc.), and provides coverage enhancements for such MTC users. In the system design, low-cost MTC users and enhanced coverage MTC users adopt a unified design scheme.
For enhanced coverage MTC UEs, it is necessary to use enhancement techniques to improve the received signal strength of the physical channel of the MTC UEs. In the discussion of Rel-12 MTC, the received signal strength of MTC physical channel is mainly improved by subframe bundling or repeat transmission. The extent of coverage enhancement that MTC UEs need in different geographical locations are different; and the MTC UEs in the same cell can be put into different coverage enhancement levels. The numbers of repeat transmissions required for different coverage enhancement levels are different; the repetition level can also be used to represent the coverage enhancement level. For example, the PRACHs of the enhanced coverage MTC UEs may be divided into four repetition levels (0, 1, 2, 3), corresponding to the coverage enhancement 0 dB, 5 dB, 10 dB, and 15 dB respectively.
In the existing LTE system, an LTE UE receives a physical downlink shared channel (PDSCH) through the control information carried by a broadband physical downlink control channel (PDCCH). Alternatively, the LTE UE may receive a UE-specific enhanced physical downlink control channel (EPDCCH) through the control information carried by the broadband physical downlink control channel (PDCCH), and then may receive the PDSCH through the control information carried by the EPDCCH. Because the MTC UE in Rel-13 can only operate at a bandwidth of 1.4 MHz (corresponding to a bandwidth occupied by 6 physical resource blocks (PRBs)/physical resource block pairs (PRB-pairs)) and the broadband PDCCH uses a 20M bandwidth (corresponding to a bandwidth occupied by 100 PRBs), the MTC UE in Rel-13 can only receive narrowband PDSCHs and EPDCCHs, but not broadband PDCCHs (hereinafter, the EPDCCH for the MTC UE in Rel-13 is referred to as MPDCCH). That is to say, the MPDCCH for an MTC UE in Rel-13 needs to fall in a bandwidth occupied by six physical resource blocks (PRBS). For the EPDCCH of the existing LET UE, the number of allocable physical resource block pairs (PRB-pairs) is 2, 4, or 8; and the allocable aggregation level is 1, 2, 4, 8, 16, or 32 (i.e., supporting aggregations of 1, 2, 4, 8, 16, or 32 contiguously distributed enhanced control channel units (ECCEs), respectively); but the number of PRB-pairs being 6 and its corresponding aggregation levels are not supported. Therefore, for the MTC UE to be adapted and operate at a bandwidth with the size of 6 PRBs, a new method for an MPDCCH transmission and reception for a narrowband MTC UE is desirable.